Amblyopia is commonly known as “lazy eye.” It is a brain and nerve defect, rather than an eye defect, so it cannot be corrected by refractive means, such as lenses. Amblyopia is the most common cause of visual impairment in children and the leading cause of vision loss in one eye in the twenty to seventy year-old age group. Amblyopia has a high occurrence rate in many countries.
In amblyopes, both eyes are usually quite normal, but the neural pathway, from the visual cortex to the eyes, is not developed completely, so the visual cortex cannot see the information from the lazy eye. A primary symptom of amblyopia is a lack of contrast sensitivity. The traditional therapy for amblyopia is occlusion (i.e., patching the normal eye for lengthy periods). But there are significant disadvantages to using occlusion therapy. The first disadvantage is that occlusion therapy is distressing to children. The second disadvantage is that occlusion is often ineffective. One-third of the children using occlusion therapy gain little or even no visual benefit, and occlusion therapy is not effective for adults. Moreover, occlusion therapy can reduce a patient's stereo acuity while not treating the patient's lack of contrast sensitivity. Despite the disadvantages, occlusion therapy is still widely practiced.